Methods and apparatus for drilling bore holes



June 22, 1965 F. L. JOHNSON 3,190,372

METHODS AND APPARATUS FOR DRILLING BORE HOLES Filed March 5, 1962 2Sheets-Sheet 1 INVENTOR. FIG. L FORD L. JOHNSON ATTOR June 22, 1965 L.JOHNSON METHODS AND APPARATUS FOR DRILLING BORE HOLES Filed March 5,1962 2 Sheets-Sheet 2 7 N J 00 JH T .N W ,m H N m 05 I (H4 L D N R W m la w w. B8 B o m m o 3 6 4 AD -w /A A /7n 6 M n e United States Patent3,190,372 METHODS AND APPARATUS FGR DRILLING BORE HQLES Ford L. Johnson,Newtown qnare, Pa, assignor to Sun M Company, Philadelphia, Pa, acorporation of New ersey Filed Mar. 5, 1962, Ser. No. 177,623 "5 Claims.(Cl. 175--2) This invention relates to new and improved methods andapparatus for utilizing explosive materials as auxiliary tools to assistconventional drillbits in more rapidly progressing through particularlyhard strata.

As described in my copending application Serial No. 86,077, now PatentNo. 3,130,797, filed January 31, 1961, shaped charges may be droppedthrough a hollow drill stem and projected through the jet openings inconventional roller or other type bits to eilect shattering of rock tofacilitate drilling. However, the use of such single charges can beconsiderably improved, in the way of shattering rock, by the addition ofa secondary charge which is not of the shaped type, but rather one whichproduces a spherical shock front. The present invention utilizes aforwardly directed shaped charge which func-' tions to blast anelongated hole extending below the drill bit and further includes asecond explosive charge which is driven into this hole and detonatedtherein so that a greatly increased volume of rock is shattered,whereupon, conventional drilling may then proceed through this shatteredportion. In this regard, it should be emphasized that the primarypurpose of the invention in using explosives is not to form the finalbore hole, but rather, to break up the hard strata so as to allow morerapid advancement of the conventional bit as well as to save wear on thebit which otherwise becomes dulled in attempting to penetrate this typeof hard formation.

In the preferred form of the invention, conventional bits are used, andthe explosive members are projected into or through one or more openingswhich, between explosions function as usual mud openings and preferablyas jet openings, the most eliective bits at the present time being ofthe jet type. Because itis the shattering effect which is desired, it isnot required that the explosions should necessarily be directed alongthe axis of the bore hole, but, rather, the major explosive energy maybe directed along the axes of conventional jet openings which are atacute angles relative to the drill stem axis.

While reference has been primarily made to conventional drilling bymeans of a rotary drill stem driving a bit, it will become evidenthereafter that the invention is applicable to hammer drills in whichflow of fluid (mud) under pressure is utilized to eifect a hammeringaction on the rock, or to turbo drills in which a rotary bit at thebottom of a drill stem is driven by a mud turbine while the majorportion of the drill stern remains stationary and serves merely as a mudconduit and support.

In summary of the advantages of the invention it may be pointed outparticularly that throughout the drilling of a complete hole the samedrilling apparatus may be used with its action augmented only where thatis required by reason of hard rock formations. When these areencountered explosions may be effected as indicated above while thedrilling proceeds without interruption. There is no need for removingthe drill stem, nor is there generally any need even for raising thedrill stem from its active drilling position. No special apparatus isrequired for taking care of debris since, even if as the result of theexplosions large sections of rock are initially produced these areground up by the operation of the drill bit and thus become fine enoughto be removed by the mud flow in completely conventional fashion. Aswill hereafter appear more clearly, the mud flow is also utilized toeffect positioning and firing of the explosive members.

It is the general object of the present invention to provide new andimproved methods and apparatus for utilizing multi-charge explosives asauxiliary tools in conjunction with conventional drill bits and, mostparticularly, with cone type bits. More detailed objects will becomeapparent from the following description when read in conjunction withthe accompanying drawings, in which:

FIGURE 1 is a diagrammatic illustration showing the upper portion of aconventional drilling rig in association with means for insertingexplosive elements in the mud flow stream;

FIGURE 2 is an enlarged showing of a conventional cone type drill bitsuitably modified for practicing the invention;

FIGURE 3 is an illustration of a first form of a multiple charge elementhereinafter referred to as a torpedo;

FlGURE 4 is a sectional view of the torpedo taken along the planeindicated by line 4-4 in FIGURE 3;

FIGURE 5 is an illustration of a second form of multiple charge torpedo;and

FIGURE 6 is an illustration of an alternative firing mechanism.

FEGURES 1 and 2 show, merely as an example, a drilling rig which issubstantially conventional and which can be used for the practice of theinvention. Many other drilling rigs may be used which may also besubstantially conventional, involving only minor changes for practice ofthe invention.

There is indicated at 2 a hook which is connected to the usualtravelling block supported by cables and controlled by the drawworks ofa derrick (not shown). A bail 4 hung on the hook supports theconventional swivel 6 modified only to the extent that its drilling mudentrance opens upwardly and its interior is provided with means forguiding the explosive members as will be evident hereafter. The swivelis joined at S with the usual kelly 10 passing through the rotary table12 by which it is driven and supporting the sectional drill stem 14 inconventional fashion. The drill stem terminates in the usual drillcollar 18. Various conventional parts of the assembly are not indicated,but it will be understood that they are provided as in usual drillingpractices.

The drill collar 18 carries a bit 29 which is illustrated as of themultiple cone type, of which one of the cones is indicated at 22. Jetopenings are provided directed between the cones, these being providedat 26 through liners 24 for resisting abrasion by the mud. In thepresent instance one of these jet openings is modified in that its liner23 is extended upwardly to provide a guiding funnel 39 which is adaptedto guide the explosive members through the opening. The funnel 30 isspaced from the walls of the central upper opening in the bit so thatmud may flow not only through the liner 28 but from the annular space 3%about the funnel through the other jet openings 26. To provide for freeflow of the mud to the space at 34 there may be provided slots in thelower portion of the drill collar as indicated at 32, the arrangementbeing such that all of the jet openings receive adequate supplies of mudto provide high velocity jets during drilling in conventional fashion.The hole being drilled is indicated at 16.

The mud flows to the swivel 6 through the flexible hose 36, beingsupplied from the usual high pressure mud pump which is not shown. Themain fiow takes place through a connection 46, but bypassed fiowto'carry the torpedoes into the hose 36, swivel 6, and the hollow drillstem takes place through a suitable loading mechanism indicated bynumeral 38. Since any number of various mechanisms may be employed toinsert the torpedoes in the mud flow pipe 36 and since the detailsthereof form no part of the present invention, a full descriptionthereof is not necessary. However, reference may be made to myaforementioned application wherein the details of such a mechanism arefully described. Briefly stated, such a mechanism includes a barrelsimilar to that employed in a revolver so that the torpedoes containedwithin the barrel successively are aligned with branch conduit 42 andthereby propelled by the mud through conduit 36 and into and through thedrill stem.

Reference is now made to FIGURE 3 which illustrates a first form oftorpedo for practicing the invention. In general, the torpedo consistsof a casing 44 which may be described as having six sections 46-56 allor some of which may be integral or provided with interengaging meanssuch as threaded portions. It should also be noted that each of thesesections may be composed of metal or shock resistant plastic so long asthey are capable of protecting the explosive material and the firingmeans from the mud, incidental shocks and the pressures existing in thebore hole. Similarly, a wide latitude of thicknesses are possible solong as the casing performs its protective function. The casing,however, should be such as to break up into small fragments assuccessive explosions occur, and for this purpose may be grooved in theconventional fashion of hand grenades.

Nose section 46 contains a centrally positioned cap 58 which isfrangible upon impact against the bottom of the bore hole, which inputwill be quite large due to the high velocity of mud flow. For example,cap 58 may be composed of a ceramic material and have a sufficientthickness to withstand the shocks occurring in handling and during itsdescent through the drill stem. However, cap 58 is sufiicientlyfrangible to be shattered upon impact with the hard rock forming thebottom of the bore hole. It should also be noted that since the torpedodoes not have a substantial velocity relative to the mud, but rather, isentrained and carried by the mud flow, the hydrodynamic shape of nosesection 46 is not critical. As a result, the nose section may berelatively blunt so that cap 58 is protected from striking funnel 3t)regardless of the angular position of the torpedo as it approachesfunnel 3t In order to control the orientation of the torpedo at thistime, a relatively long tail section 56 is provided so that the torpedomaintains a substantially vertical or axial position during its descent.Since the maximum angle of derivation from the vertical can bedetermined by the length of the tail, the shape of the nose section 46as well as the curvature of funnel 350 may be designed to positivelyprevent cap 53 from contact with the funnel.

As further shown in FIGURE 3, cap 53 receives end 69 of a rigid firingpin 62, the pin extending centrally through sections 46, 48, th, 52 and54. Since a single firing pin is utilized to detonate all of the chargesas well as the propellant, as will be more fully described hereinafter,a safety pin 64 may be passed through nose section 46 and pin 62 so thatit positively prevents accidental movement of the firing pin prior tothe insertion of the torpedo in the loading mechanism at which time thesafety pin may be removed and the torpedo becomes semiarmed.

Immcdiately above nose section 46 there is located a shaped charge 66which is confined at the forward end by a conical retainer 68. As iswell known in the art of shaped explosives, retainer 68 may be in one ofvarious forms each form being particularly designed to create a cavityof a particular shape. In this regard, the major requirement is thatshaped charge 66 be designed so as to create a cavity having a depth anda diameter sufficiently large to permit the entry of high explosivesection 52. In addition, it is of course desirable to produce a cavityhaving a depth greater than the length of section 52 in order to achievea maximum amount of shattering upon detonation of section With theseparameters in mind, charge 66 may be designed so that the angle of cone68,

the stand-off distance between the apex of cone 68 and the tip of cap 53and the location of the detonator 74 are suitable for achieving theseobjectives.

A detonator 7d is provided in the form of a cap which threadedly engagescylinder portion 72 of cone 68. Firing pin a2 is provided with anenlarged head 74 which is located in detonator 7t) and positioned at thelower end thereof, the remaining portion of the detonator being filledwith an impact-sensitive detonation material which is fired uponmovement of head 74. The upper end of charge 66 is enclosed by a pair ofrelatively thick diaphragms 76, 78 between which there is provided ahighly shock absorbing material 80, For example, this may be a plasticfoam material containing sealed air pockets which disrupt the shockfront and impede the velocity of portions thereof so that destructiveinterference effectively destroys the shock wave in the upwarddirection. Of course, it should also be noted that the amount of shockabsorbing material and the thickness of diaphragms 76 and 78 is directlyproportional to the efficiency of shaped charge 66. In this type ofcharge it is actually possible to have substantially all of theexplosive force directed forwardly, downwardly as viewed in FIGURE 2, sothat a very minimum of such shock absorbing means are necessary toprotect the high explosive section 52. That is, so long as the explosivewithin section 52 is of the non-impact type, the detonation of theshaped charge may be safely accomplished without detonation of the highexplosive.

Diaphragm 73 performs the additional function of cooperating withdiaphragm 82 and easing section to provide a housing for a secondarysafety mechanism 84. This mechanism includes a piston 86 the outer endof which is exposed to the well fluids and the inner end of which isbiased outwardly by spring 88. Piston is provided with an elongated slot90 through which firing pin 62 passes. However, the firing pin isprovided with a radially extending lug 92 immediately below piston 86 sothat, when the piston is biased to its rightmost position as illustratedin FIGURE 3, lug 92 is prevented from moving upwardly through slot 90.On the other hand, when the torpedo has descended to a depth wherein thepressure of the well fluid is sufiiciently high to displace piston 86 tothe left against the preset biasing force of spring 88, lug 92 is thenunlocked and the torpedo is fully armed. Thus, safety mechanism 84performs the very desirable function of positively preventing detonationuntil the torpedo has proceeded a safe distance from operating personnelat the surface even though the primary safety pin 64 has been removedprior to its descent.

Immediately above safety mechanism 84- there is positioned the highexplosive section 52 which is enclosed at its lower end by diaphragm 82and at its upper end by diaphragm 94 both of which may be integral withcasing section 52. A cylinder 96 is provided with one end threadedlyengaged in diaphragm 32 and its upper end threaded for the reception ofdetonator casing 98 thereby rigidly securing the latter in position.Detonator 9-8 is surrounded by .a suitable high explosive material suchas TNT or the like which is not impact-sensitive so that it is notdetonated upon the detonation of shaped charge 66. In order to providefor the delayed detonation of section 52, detonator 98 includes a layerconsisting of a small amount of impact-sensitive ignition material 160surrounding the enlarged head 102 of firing pin 62. A suitable delaytrain tiltof slow burning powder is provided immediately above ignitionmaterial and, in turn, a main detonator material 1% is positionedimmediately above the delay train. Casing 98 is designed so that thehigh explosive is not detonated upon ignition of igniter material 16-6,but rather, is only detonated upon the ignition of detonator material 1%as is conventional in such explosive primers.

Immediately above high explosive section 52 there is provided apropellant section 54 containing a suitable propellant material Kid. Thepropellant 133 is slower-burning than the very high burning rate shapedcharge explosive material, so that, even though simultaneously ignited,time delay occurs as brought out later. Since it is necessary thatcasing 54 contain the propellant after its ignition and throughout itsburning period, it should be noted that casing 54 is relatively thickerthan the casing sections housing the explosive charges. It will also benoted that the interior surface of casing 54 may be formed as a reactionnozzle 109 of the convergent-divergent type in order to obtain maximumthrust from the propellant. Means for igniting the propellant areprovided in the form of a cup-shaped member 110 supported by a web 112secured to the inner surface of the-nozzle. Cup 1-10 contains ignitionmaterial 1 14 of the impact-sensitive type so that propellant 108 isignited upon upward movement of firing pin 62. It will be readilyunderstood that cup 110 and web 112 are of light construction since theyonly serve to contain ignition material 114 prior to detonation.Thereafter, they are disintegrated by the intense heat of the burningfront of the propellant and discharged outwardly through the nozzlealong with the other propella-nt products.

Reference is now made to the aft section 56 which is composed of arubber, aluminum, or other lightweight casing which may be provided witha central cavity 116 filled with air or other inert gas. The purpose ofthis aft or tail section is to guide the torpedo through the drill sternand prevent it from assuming an angular position relative to thevertical axis of the drill stem whereby it might engage funnel 30 andcause a detonation within the drill bit. Tail 56 is preferably made asbuoyant as possible so that the torpedo remains in a vertical positionthroughout its descent through the stem and therefore becomes readilyentrained in the mud flowing through the stem and jet 28. In addition,the tail portion serves as a piston or plunger when the torpedo hasassumed the position shown in FIGURE 2 wherein the high pressure fluidacts upon the end of tail 56 and forces cap 58 against the bottom of thebore hole with considerable force and velocity so that detonation isassured.

Lastly, it will be noted that the mutually engaging ends of sections 52,54 and 56 are provided with threaded portions 118 and 120, respectively.Similarly, firing pin 62 is provided with a separable section 1-22 whichis threaded to the lower portion of the firing pin so that propulsionsection 54 may be removed and tail section 56 may be threaded to the aftend of section 52. For this reason, section 56 is provided with a slot124 so that, in the event propulsion section 54 is not employed, the aftend of firing pin 62 will terminate in cavity 124. Thus, the torpedo isdesigned for use with or without propulsion section 54- the reason forwhich will be more fully set forth in the description of operation,

Ordinarily, the drilling through relatively soft formations will proceedin the usual fashion without the aid of explosives and the use of thepresent method does not involve any deviations from the normal practiceemployed in rotary drilling wherein conventional, cone-type bits areutilized for the most rapid rate of drilling progress. The jet openingsin the bit perform their normal function of assisting the rollers byflushing the cuttings and also by the jet action of the mud flow whichtends to assist the bit in cutting the well bore. Insofar as thestructure of the drilling rig is concerned, the only matter which needbe taken into account in the practice of the invention is that the mudhose should have a sufiiciently large radius of curvature so that itdoes not impede the free movement of the torpedoes therethrough whenthey are used. Thus, ordinarily the major portions of the of drilling isslowed down by the encountering of hard strata. This will be evidencedquite promptly by observation of the downward movementof the drill stem.When this occurs, safety pin 64 is removed from one of the torpedoes andthe torpedo is introduced into the mud line by the means of the loadingmechanism 38. During the period of introduction of the torpedo and thetime of its descent to the location of the bit, drilling may becontinued, continuation having no adverse effect with reset to theexplosive operation.

The torpedoes may range from substantially heavier to substantiallylighter than the mud depending upon the buoyancy of tail 54, however, itis preferable to have the torpedos as a whole somewhat heavier than thedisplaced mud in order to speed their rate of descent. Actually, thespeed of descent in either case will approximate rather closely the rateof mud flow. Accordingly, the torpedo becomes entrained in the mud flowand the buoyancy of tail section 54 relative to the forward portions ofthe torpedo will tend to keep it axially aligned and prevent any violentengagement with the internal surface of the drill stem through which itpasses as at the drill stem joints. However, the torpedo may glance offthe internal surface of the drill stem without any possibility ofexploding. Arming occurs, when a suificient pressure is encountered, bythe inward movement of piston 84. As previously indicated, the entirecasing structure is sufficiently strong to resist the pressure increaseand is also sufiiciently strong to withstand the above-mentionedglancing impacts. Thus, the firing pin remains unmoved during thedescent and, as also stated hereinabove, the location of cap 53 and therelatively blunt shape of nose section 46 prevent firing of the torpedoby impact with funnel 130. The torpedo passes through the funnel, beingguided thereby, and enters the jet opening defined by liner 28. Sincethe mud flow is continuing, the velocity of the torpedo will beincreased as it passes through the jet opening and it will be ejected atan extremely high velocity so that there is virtually no possibilitythat cap 58 will not be shattered upon impact with the rock strata atwhich time firing pin 62 is forced upwardly relative to the torpedocasing.

. At this point it must be noted that the following events occursimultaneously from a macroscopic view point, however; in order tounderstand the operation of the invention, it is necessary to describethe events in a greatly exaggerated degree of slow motion, the actualtime intervals between various events being measured in milliseconds.First, it will be appreciated that the torpedo as a unit hasconsiderable momentum at the instant of impact between the forward endof cap 58 and the rock strata. Thus, firing pin 62 is driven rearwardlyrelative to the casing which continues in the forward direction.Secondly, it will also be noted that tail portion 54 is contained withinliner 23 at the instant of impact so that the torpedo acts as a plug inthe jet opening of the bit having considerable pressure exerted by themud on its tail portion which further aids the propulsion of thetorpedo. Thirdly, the dimensions of the firing pin are chosen such thatpin 62 extends forwardly beyond the edge of nose 46 for a distance whichis considerably greater than the amount of displacement of the pin whichis necessary to detonate the detonators 7t 1% and This design, althoughnot absolutely necessary, greatly increases the resultant effect byallowing shaped charge 66 to explode and create the necessary cavity inthe rock strata while the remainder of the torpedo still retainsconsiderable momentum and is therefore more easily driven into thecavity formed by the shaped charge.

Referring again to the instant of impact, it will be noted that allthree detonators are simultaneously fired so that propulsion section 54is ignited at the same time that shaped charge 66 is detonated. However,because of its slower burning rate'the propellant exercises its drivingeffect only after the action of the shaped charge has been completed.Ignition of the propellant immediately separates the forward portion ofthe torpedo from tail portion 56 which is connected th reto by therelatively weak connection provided by threads 126 At this point itshould also be understood that propellant section 54 may or may not beemployed depending upon various factors including the depth at which thebit is operating and the amount of explosive material utilized in chargees. if the depth is sufficiently great so that an extremely highpressure of the mud is exerted against tail section 56, this may besutficicnt to drive the high explosive section 52 into the cavity formedby the shaped charge, the latter being sufiiciently small and accuratelydesigned so that substantially the entire force is directed forwardly toshatter the rock and very little energy is left to react upon theremaining portion of the torpedo. in either event, high explosivesection is driven into the cavity formed by shaped charge so and thehigh explosive section explodes after it is located therein. This isaccomplished by means of the interposition of delay train 164 betweenignition material 1% and detonator material 1%.

As previously stated, the time period between detonation of the shapedcharge and the high explosive section may be in the order of thousandthsof a second so that delay train Mid may have a very short delay time.

From the foregoing escription it will be apparent that the presentinvention provides a marked divergence from what is described in raycopending application in that the purpose of shaped charge so is tocreate a hole for the reception of the high explosive section, thelatter performing the actual shattering of the rock whereby the progressof the drill bit is substantially increased over the result previouslyobtained by utilizing the shaped charge alone as the rocl: shatteringexplosive.

It may be noted that because the action of the shaped charge in forminga hole is followed by the driving of the high explosive into the hole bya matter of only milliseconds, even though the at is continuouslyrotating there is maintained, for all practical purposes alignment ofthe jet opening with the formed hole during the sequence of explosiveevents.

Reference is now made to FEGURE 5 which illustrates a second form ofmultiple charge torpedo for practicing the invention. This form differsfrom that previously described in that it employs an electrical firingsystem rather than the mechanical impact type just described. Thisembodiment employs an electrically conductive casing I139 having a nosesection 7.32 which threadedly receives an electrically conductivecylinder 134. A firin: plunger res which is also composed of anelectrically conductive material is received within cylinder f 3 and maybe provided with an O-ring seal to prevent the entrance of well fluids.A safety pin is received in cylinder 134 and passes through plunger 136in order to prevent accidental displac ment of the plunger prior to itsentrance into the loading mechanism The upper or rearward end of plunger136 is formed of a reduced diameter and surrounded by a snap actionspring the periphery of which is engaged in an annular roove in cylinder134. Immediately above the plunger there is elongated electrode 142 thelower end of which is spaced from the upper tip of the plunger therebyforming a snap action switch as will be more fully explainedhereinafter. The upper end of electrode 142 is secured to cone 144 whichforms a conical retaining wall for the explosive material 146 comprisingthe shaped charge 143. This charge further includes a detonator lS-tlwhich comprises a casing 1513 containing suitable detonation materialand two spaced electrodes -1, 156 joined by a filament E58. Electrode154- is connected to liner and electrode 142 by means of a suitablyinsulated lead 16% passin through the explosive material 146. It will benoted that liner 144 is insulated from casing 13%? by the interpositionof insulator ring M5. Electrode 56 is connected by an insulated lead 162to contact 171 located in diaphragm 16$ but insulated therefrom. Acapacitor Lid is insertable in bore 165 and are adapted to be sealedtherein by plate 101:. Capacitor 164 is provided with an insulatingcasing 176) having exposed terminals i713 and 174- which connect theplates of the capacitor to contacts 172 and 176, respectively. Contact176 is positioned in diaphragm but is suitably insulated therefrom. Inturn, contact 176 bears against the surface of pressure responsivepiston 132 which includes a radially inner portion composed of aninsulating material and a radially outer portion 1% composed of anelectrically conductive material. Upon increase of pressure in the Wellas the torpedo descends, conductive portion 186 bridges contacts 176 and18 3 thereby establishing a circuit from lead 162 to lead 188. Thus,this mechanism serves the same function as that of mechanism 84previously described.

High explosive section M9 is positioned immediately above the safetymechanism and consists of a suitably sized charge 192 of a non-impacttype explosive material surrounding a three part detonator 194.Detonator 194 is identical to detonator 93 previously'described exceptfor the substitution of electrodes 185, 187 and filament 189 in place ofthe mechanical firing pin. Detonator 94 provides the desired timeinterval between detonation of charges 14% and 192 by reason of delaytrain 1% which functions in a manner identical to delay train 134 aspreviously described.

Above the hi h explosive section there is provided a propulsion section1% containing propellant 199. This section is identical to propulsionsection 54 previously described except for the substitution ofelectrodes 294), 2% and filament 264 in place of mechanical firing pin62. It will be noted that electrode 202. is connected to casing whichthereby completes the circuit back to plunger 136.

The operation of this embodiment is as follows. Capacitor 164 is chargedand inserted into the circuit wherein it is retained by cover plate 168just prior to use. Upon engagement or" plunger 136 with electrode 142,capacitor 164 discharges causing filaments 153, 189 and 294 tosimultaneously ignite their respective detonators. This causessimultaneous detonation of charge 148 and ignition of propellant 199 sothat a cavity is produced into which charge 192 is propelled andexploded.

It will also be noted that this embodiment provides for the removabilityof propulsion section 198 and the alternative connection of tail section208 to the upper end of the high explosive section by reason of threadedportions 210 and 212. Thus, the employment of this embodiment isidentical to that previously described and the operation thereofproduces the same high degree of rock shattering as does the firstembodiment.

Reference is now made to FIGURE 6 which illustrates a magneticallyresponsive actuating system which may be employed in place of or inaddition to the impact type actuating means 58 and 136 or FIGURES 3 and5, respectively. FIGURE 6 illustrates the same condition as illustratedin FIGURE 1 wherein tail section 298 of the torpedo is within liner 28at the instant of impact with the bottom of the bore hole. In thisembodiment, a plurality of permanent magnets 22% are circumferentiallydisposed in the Walls of liner An additional permanent magnet 222 ispivotally supported by shaft 224 and biased into a positionperpendicular to the longitudinal axis of tail section 2-03 by means oftension springs 226 secured to diaphragm 2Z8. Magnet 222 thereforeremains in this position irrespective of axially or radially directedimpacts occurring during the descent of the torpedo. Iowever, when thetorpedo is positioned such that the poles of magnet 222 are centeredbetween the poles of magnets 22%, the four magnetic forces of repulsionand attraction become additive so that magnet 222 is forcibly rockedabout piVOt shaft 224- in the direction of the arrow shown in FIGURE 6.This movement is communicated to rod 239 which may be secured to magnet222 or shaft 224 and the movement of rod 236 may be utilized to closethe firing circuit of the FIGURE 5 embodiment or to mechanically actuatefiring pin 62 of the FIGURE 1 embodiment. If

utilized with the latter embodiment, a compression spring may beinserted between end 60 of firing pin 62 and cap 58 and rod 230 may beconnected through suitable linkage to remove an additional pin operatingin the nature of pin 64 to release firing pin 62.

Since numerous modifications and/ or alterations will become readilyapparent, it is to be understood that the foregoing embodiments areintended to be illustrative rather than exhaustive and that theinvention is not to be limited otherwise than as set forth in thefollowing claims.

What is claimed is:

1. The method of drilling a bore hole through earth strata comprisingthe steps of:

effecting rotary drilling with a hollow drill stem driving a drill bithaving a solid central portion and a nonaxially aligned jet opening toform a bore hole of a first depth,

introducing a multiple charge torpedo into said hollow drill stem at thesurface of the bore hole,

effecting axial passage of said torpedo downwardly through said hollowdrill stem to the vicinity of said bit,

orienting said torpedo so as to pass at least partially through saidnon-axial jet opening to arrive at a position adjacent the earth strataforming the bottom of said bore hole,

detonating a first charge of said multiple charge torpedo to form acavity in said strata forming the bottom of said bore hole,

explosively propelling a second charge of said multiple charge torpedointo said cavity,

detonating said second charge to eifect fracturing of the materialforming said cavity, and

continuing rotary drilling through said strata by said drill bit.

2. The method of drilling a bore hole through earth strata comprisingthe steps of:

effecting rotary drilling with a hollow drill stem driving a drill bithaving a solid central portion and a nonaxially aligned jet opening toform a bore hole of a first depth,

introducing a multiple charge torpedo into said hollow drill stem at thesurface of the bore hole,

entraining said torpedo in flow of drilling fluid to pro pel it at leastpartially through said jet opening to arrive at a position adjacent theearth strata forming the bottom of said bore hole,

detonating a first charge of said multiple charge torpedo to form acavity in said strata forming the bottom of said bore hole,

explosively propelling a second charge of said multiple charge torpedointo said cavity,

detonating said second charge to etfect fracturing of the materialforming said cavity, and

continuing rotary drilling through said strata by said drill bit.

3. Apparatus for drilling a bore hole comprising in combination:

mechanical drilling means,

said drilling means including a drill stern and a drill bit secured tothe lower end of said stem,

an axially extending passage in said drill stem,

at least one jet opening extending through said bit in a 10 directiontransverse to said drill stern passage and in fluid communicationtherewith, a multiple-charge torpedo of a size sufficiently small topass through said passage and said jet opening,

guiding means within said drilling means for effecting .the passage ofsaid torpedo from said passage into said transverse jet opening and atleast partially through said jet opening to a position adjacent thebottom of the bore hole,

means for detonating a first charge of said multiplecharge torpedo toform a cavity in the bottom of said bore hole,

explosive means for eifecting the entrance of a second charge of saidmultiple-charge torpedo into said cavity, and

means for detonating said second charge to produce explosive shatteringof the material surrounding said cavity.

4. The apparatus as claimed in claim 3 wherein the said first charge isa shaped charge.

5. Apparatus for drilling a bore hole comprising in combination:

mechanical drilling means,

said drilling means including a drill stern and a drill bit secured tothe lower end of said stem,

an axially extending passage in said drill stem,

at least one jet opening extending through said bit in a directiontransverse to said drill stern passage and in fluid communicationtherewith,

a multiple-charge torpedo of a size sufiiciently small to pass throughsaid passage and said jet opening,

guiding means within said drilling means for eifecting the passage ofsaid torpedo from said passage into said transverse jet opening and atleast partially through said jet opening to a position adjacent thebottom of the bore hole,

means for maintaining said torpedo in a substantially vertical positionduring the descent thereof through said drill stem passage,

means for detonating a first charge of said multiplecharge torpedo toform a cavity in the bottom of said bore hole,

explosive means for effecting the entrance of a second charge of saidmultiple-charge torpedo into said cavity, and

means for detonating said second charge to produce explosive shatteringof the material surrounding said cavity.

References Cited by the Examiner UNITED STATES PATENTS 1,511,488 10/24Alexander 102-20 1,585,664 5/26 Gilman -2 2,307,729 1/43 Foster 175-22,416,077 2/47 Yuster 102-20 2,809,585 10/57 Moses. 2,869,825 1/59Crawford. 2,898,085 8/59 Borins et al. 175-2 2,910,000 10/59 Brandt102-56 3,047,796 7/62 Bennett et al. 175-50 3,070,010 12/62 Robinson175-2 3,083,778 4/63 Friedman et al. 175-2 CHARLES E. OCONNELL, PrimaryExaminer,

1. THE METHOD OF DRILLING A BORE HOLE THROUGH EARTH STRATA COMPRISINGTHE STEPS OF: EFFECTING ROTARY DRILLING WITH A HOLLOW DRILL STEM DRIVINGA DRILL BIT HAVING A SOLID CENTRAL PORTION AND A NONAXIALLY ALIGNED JETOPENING TO FORM A BORE HOLE OF A FIRST DEPTH, INTRODUCING A MULTIPLECHARGE TORPEDO INTO SAID HOLLOW DRILL STEM AT THE SURFACE OF THE BOREHOLE, EFFECTING AXIAL PASSAGE OF SAID TORPEDO DOWNWARDLY THROUGH SAIDHOLLOW DRILL STEM TO THE VICINITY OF SAID BIT, ORIENTING SAID TORPEDO SOAS TO PASS AT LEAST PARTIALLY THROUGH SAID NON-AXIAL JET OPENING TOARRIVE AT A POSITION ADJACENT THE EARTH STRATA FORMING THE BOTTOM OFSAID BORE HOLE, DETONATING A FIRST CHARGE OF SAID MULTIPLE CHARGETORPEDO TO FORM A CAVITY IN SAID STRATA FORMING THE BOTTOM OF SAID BOREHOLE, EXPLOSIVELY PROPELLING A SECOND CHARGE OF SAID MULTIPLE CHARGETORPEDO INTO SAID CAVITY, DETONATING SAID SECOND CHARGE TO EFFECTFRACTURING OF THE MATERIAL FORMING SAID CAVITY, AND CONTINUING ROTARYDRILLING THROUGH SAID STRATA BY SAID DRILL BIT.